Defrosting evaporators



Nov. 6, 1956 T. w. DUNCAN DEFROSTING EVAPORATORS 6 Sheets-Sheet l FiledJuly 2, 1953 ii @i INVENTOR.

Nov. 6, 1956 T. w. DUNCAN 2,769,311

DEFROSTING EvAPoRAToRs Filed July 2, 1953 e sheets-sheet 2 NOV 6, 1956T. w. DUNCAN DEF'ROSTING EVAPORATORS 6 Sheets-Sheet 5 Filed July 2, 1955Nov. 6, 1956 T. w. DUNCAN DEFRosTING EvAPoRAToRs 6 Sheets-Sheet 4 FiledJuly 2, 1955 Nov. 6, 1956 6 Sheets-Sheet 5 Filed July 2, 1953 ISCHARGECOHPKE550R LINE INVENTOR.

Filed July v 2, 1953 6 Sheets-Sheet 6 ln* l l i l t dv 1) L 1 INVENTOR.of/zza WMM WW United States Patent O DEFROSTING EVAPORATORS Thomas W.Duncan, Bedford, Ind., assignor, by mesne assignments, toWhirlpool-Seeger Corporation, a corporation of Delaware Application July2, 1953, Serial No. 365,694

6 Claims. (Cl. 62-3) The present invention relates to defrostingevaporators, and is particularly concerned with an improved form ofdefrosting evaporator of the same general type covered by the priorapplication of Thomas W. Du-ncan and Albert C. Rosencranz, Serial No.242,462, filed August 18, 1951, for Automatic Defrosting Evaporators,now Patent No. 2,654,226.

One of the objects of the invention is the provision of an improvedconstruction for defrosting evaporators by means of which the coldestpart of the evaporator is defrosted last, so that the frozen articlesstored therein are subjected to the least amount of heat.

Another object of the invention is the provision of an improvedevaporator of the type in which the refrigerant may be caused tocirculate during the defrost part of a cycle by the action of heatapplied at a particular area of the evaporator, heating the refrigerantwhich is then circulated throughout the entire evaporator.

Another object of the invention is the provision of an improvedevaporator fluid circuit, including a header for the suction tube inwhich the evaporator conduits are designed in the form of a completeloop connected at both ends to the header, and provided with portions ofsubstantially equal resistance to flow so that by the application of aheater to an intermediate part the heated refrigerant can be caused tocirculate throughout substantially the entire length of the evaporatorconduits to heat the evaportor uniformly and melt the frost off `all itsareas within a short time.

Another object of the invention is the provision of an improvedevaporator heating arrangement which heats the evaporator by heating therefrigerant, and which is adapted to effect a defrosting of theevaporator so quickv ly that the food which is stored in the evaporatoror in the food storage space will remain substantially in its previouslyfrozen state without being damaged by the introduction of heat into theevaporator.

Another object of the invention is the provision of an also in serieswith each other from one header connection to the `other headerconnection of the conduits.

Another object of the invention is the provision of an improveddefrosting evaporator which provides a quick freeze s'helf for freezingice cubes and a relatively large frozen food storage space equallyadaptable tothe storage of frozen food, or the initial freezing of thefood, which is Vsimple in construction, capable of economicalmanufacture and adapted to perform its functions for a long period oftime without necessity for repair.

Other objects and advantages of the invention will be apparent from thefollowing description and Vthe accompanying drawings, in which similarcharacters of reference indicate similar parts throughout the severalviews. Y

Referring to the drawings, of which lthere are six sheets accompanyingthe specification,

ICC

Fig. l is a fragmentary front elevational View of a r'efrigeratorcabinet equipped with an evaporator embodying the invention with theevaporator door removed;

Fig. 2 is a fragmentary side elevational view of the upper part of therefrigerator equipped with such an evaporator;

Fig. 3 is a top plan view of the evaporator;

Fig. 4 is a side elevational view taken from the bottom of Fig. 3;

Fig. 5 is a fragmentary rear elevational view of the evaporator;

Fig. 6 is a front elevational view of the evaporator door;

Fig. 7 is a side elevational View of the evaporator door;

Fig. 8 is a fragmentary section taken on the plane of the line 8 8 ofFig. 2;

Fig. 9 is a diagram of the refrigeration system ernployed in theevaporator;

Fig. l0 is a wiring diagram of one form of control for the defroster.

Referring to Figs. l Vand 2, 10 indicates in its entirety a defrostingevaporator embodying the invention, which is shown installed in arefrigerator cabinet 11, having an outer shell 12, and an inner liner 13separated from the outer shell by insulation 14.

The cabinet is provided with an inwardly turned facing ilange 15 on itsouter shell surrounding a door opening 16, and the opening is closed bya suitable insulated door 17, having an inner panel 18 and an outerpanel 19, separated by insulation 20.

The door carries a suitable resilient seal 21, engaging the facingllange 15, all around the door opening a-nd assuring an airtightclosure.

The evaporator 10 may be wide enough laterally to occupy substantiallythe full width of the upper part of the cabinet, and may comprise arectangular sheet of aluminum which is bent to form a substantiallyU-shaped member having side walls 22 and 23, joined by easy bends 24 and25 to the integral bottom wall 26.

Evaporator walls 22 and 23 are ben-t backwardly upon themselves at theirupper edges to form a smooth upper edge 27, by means of the backwardlybent flange 28.

At the front edge the side walls 22 and 23 are also bent backwardly atthe llange 29, the bend forming a smooth front edge surface 30 whichalso extends across the front edge of the bottom 26. The flanges 28 and29 are mitered at 31, where they meet at the top front corner, Fig. 2.

While the blank sheet of which the evaporator is made is substantiallyrectangular, the side walls 22 and 23 are preferably slightly longer atthe back, making the side walls trapezoidal, causing the bottom 26 toslope downward toward the back when the evaporator is installed with itsupper edges in horizontal position in a cabinet having a horizontalliner top 34.

Upper edges of the two side walls are provided with pairs of anglebrackets 32, 33, one flange of which is riveted to the side walls of theevaporator, and the horizontal flange of each bracket is secured to thetop wall 34 of the liner.

The liner may have four evaporator hanger supports Welded on the outsideof the liner above the brackets 32, 33. Each hanger support comprises astrip of steel with an easy bend to fit the corner of the liner, andhaving a threaded tubular formation 32a for receiving screw boltspassing through the brackets and through a registering hole in theliner.

Thus the evaporator may be installed with its top edges substantiallyhorizontal and its bottom wall 26 and its shelf both sloping downwardtoward the back, and the top of the liner closes the top of theevaporator.

The back of the evaporator is preferably closed by means of a back plate35 of aluminum, comprising a plate of sufficient size to cover the back,the plate being provided with forwardly extending attaching flanges 36,37, for each side wall, and being secured to the side walls by means ofa plurality of rivets 3S.

A bottom attaching llange 39 also engages below the bottom wall 26 andassures a substantial closure of the rear side of the evaporator. 35conforms substantially in shape to the U-shape of the evaporator withits rounded corners 24, 25 about which the attaching lianges fitsinuously.

At its upper edge the back plate 35 may have a rear- The rear evaporatorplate wardly turned horizontal ange 40 engaging the top of the liner.The upper edges of the side walls and back plate of the evaporator havea substantial lit against the walls of the liner so that the top of theevaporator is closed by the liner.

The side walls 22 and 23 of the evaporator support an upper shelf 41,which is preferably spaced from the top of the evaporator by a distancesuitable for receiving ice trays.

The shelf is substantially rectangular in shape, having a lengthcorresponding to the width of the evaporator and having a front to backwidth corresponding to the front to back depth of the evaporator.

At each side the shelf 41 is provided with a depending attaching flange42, which is secured by rivets 43 to the side walls 22 or 23. At itsback edge the shelf 41 is Y provided with an upwardly extendingattaching flange 44 engaging the inside of the back` panel 35, to whichit is secured by rivets 45.

At its forward edge the Shelf 41 is provided with a depending ange 46,having its edge backwardly turned at 47. The depending and backwardlyturned flange 46, 47 gives the shelf a more substantial appearance andpresents a blunt or flat forward facing, and also conceals the coilsfrom an observer whose eyes are substantially at the level of the shelfor above the shelf.

The back panel 35 may be provided with a multiplicity of circularapertures 48, located at the bottom level 26 so that any moisturecollecting on the bottom 26 will drain downwardly and backwardly out ofthe apertures 48.

The side wall 23 is preferably formed with an elongated, oval aperture49, having parallel upper and lower edges 50 and 51, and rounded endportions 52 adjacent a stamped partially cylindrical groove 53 andgroove 54.

In order to drain the shelf, the back panel is provided with a pluralityof shelf drain apertures 48a, located just above the shelf level.

The front groove 53 terminates in a rounded end 55, short of the frontedge of the evaporator, but the rear groove 54 may extend to the backedge of the side wall 23. The purpose of the oval aperture 49 andgrooves 53, 54 is to house a receiver or header 56, which issubstantially complementary in its diametrically located outline fromend to end.

The header 56 comprises a substantially cylindrical aluminum tube 57,which has its tapered end portions 5S and 59 spun inward to provide asubstantially tubular conduit 69 at the rear end and to provide aclosure 61 at the front end.

rl`he receiver 56 is provided with spaced integral diametrically locatedattachment anges 62 at the top, and 63 at the bottom. These attachmentflanges engage the outside of the side wall 23 when the receiver isdisposed in the oval aperture 49, and the attachment anges are rivetedto the side wall 23 by rivets 64, 65.

The receiver 56 is provided with a suction tube 66, which extends intoits top wall and terminates at 67, close to the inside of the top wallfor sucking olf vapor which will be located at the top of the receiverabove any liquid refrigerant in the receiver.

The suction tube 66 extends parallel to the top of the receiver 56 at63, and at the rear end of the receiver it is bent and provided with adownwardly extending portion 69, and with a forwardly extending portion70, leading to the inlet of the compressor which is used to supply theevaporator with liquid refrigerant and which draws olf the refrigerantvapor.

The sides and bottom of the evaporator are provided with sinuous coils71, 72, 73, Figs. 2 and 4. For example, the sinuous coils 71 maycommunicate with the inside of the receiver 56 at 74, from which thecoils '71 extend backward at 75 and have a hairpin bend at 76. Theyextend forward and downward at 77, and have a hairpin bend at '78 andextend backward and downward at 79.

At the coils 71 are bent downward and are bent under the bottom at 81.The coils extend sinuously back and forth from side to side across thebottom at 72, with the same easy bends adjacent each side wall,terminating at the bottom, near its front edge at 82, where the coilsare curved upwardly at 83 on the outside of the side wall 22.

Here again the coils 73 extend horizontally at 84, have an easy bend atS5, horizontally at 86, with an easy bend at 87. horizontally at 8S,with an easy bend at 89, and a horizontal portion at above the shelf 41.

The arrangement and distribution of these coils is such that every partof the side Walls has contact with some of the coils in proportion tothe amount of frost which is likely to gather thereon, and when thecoils contain heated refrigerant they effectively melt all of the frostfrom the side walls and bottom.

At 91 the side coils 73 are bent downward with a diagonal portion 92that extends to an aperture 93 in the side wall 22, near its rear edgeso that the coil may extend into the evaporator for arrangement on thelower side of the shelf.

The coils on the bottom of the shelf have been indicated in theirentirety by the numeral 94, and beginning at the aperture 93, Fig. 3,the shelf coils include a straight pass 95, adjacent the front ange 46of the shelf for eX- tending the cooling action and melting action wellforward on the shelf.

Thereafter the coil on the bottom of the shelf has an easy bend at 96, aparallel lateral pass at 97, easy bend at 98, and another side to sidepass at 99. This leads to an easy bend at 1119 and a straight side toside pass 191, an easy bend at 102, and a straight pass 1113, whichstops short of the side wall 23 at a U-shaped easy bend 104, from whichthere is a straight pass 195 extending laterally of the bottom of theshelf adjacent the rear panel 35 and passing through the side wall 23 atan aperture 106.

From the aperture 106 the tubing is bent downward of the side wall 22,Fig. 4, and has a straight pass downward indicated at 107. The straightdownward pass 107 is bent at 108 to conform to the curvature of theshell and extends inwardly along the bottom of the evaporator at 109,with a Asubstantially straight pass which is bent backwardly at 110,leading to a backwardly and downwardly extending diagonal portion 111.

The tube is bent downward at 112 and communicates with a verticallyextending portion 113. This extends to a U-shaped bend 114, which has anupwardly extending short tube 115. Tube 115 communicates with a tubularextension 116 of an enlargement or receiver 117, which extends parallelto the tube 113.

Receiver 117 comprises a tubular member having its end portions spundown to be tapered at 118 and pro* vided with the tubular formations 116and 119. The upper tubular formation 119 is connected by a diagonalportion 120, with a laterally ex-tending pass 121, Fig. 3 at the bend122.

' The laterally extending pass 121 extends across the bottom to .theside 23, and is provided with an easy bend at 123 and extends upward at124.

The upwardly extending portion 124 is shown in Fig. 2

toward the rear wall 35, and it extends upward on the side wall 23 tothe point 125, whereit is .bent at an obtuse angle having a diagonallyextending portion 126 to permit an easy bend at 127, leadingto'thehorizontal portion 128 which extends into` the tubular endv 129 of thereceiver 56.

Thus the depending legs 113, 117 extend on the right side of theevaporator up to the receiver 56,' and on the left side of theevaporator the leg 113 extends over across the bottom and upward to theshelf. l

The enlargement `117 is provided 'with an integral metallic clampingmember 130, which may also comprise a member welded or brazed totheenlargementv117 of substantially U-shape for receiving and clampingabout a tubular, metal encased electrical resistance used as a heater.Such electrical heaters include a resistance wire which is surroundedand insulated by a heat resistive powder and which may be encased withan aluminum or copper tubing.

A thermostatic switch has its bulb attached to the leg 113 near the topof the leg land adjacent the electric heater 130g, for the purpose ofcuttingoif the electricheater and restoring the `system to normalrefrigeration control when the bulb reaches a predetermined temperature.

Ordinarily defrost may be terminated by this switch when the circulatinghot refrigerant which goes up the leg 117 has traversed the entireevaporator and arrived in a hot condition at the bulb 113a at sufficienttemperature to raise the bulb to lthe cutoff temperature.

At this time the entire evaporator will have been heated sufficiently tomelt ol all the' frost. In the case of a failure of circulation of therefrigerant, the bulb may be sufficiently heated by conduction andradiation from the heater 130g, due to its proximity to the`heater, tocut otf `the electric heater before any damage is done.

The bulb 113:1 is connected by a small bore to a bellows which actuatesa switch'and is preferably charged with a sub-atmospheric charge ofrefrigerant or other volatile gas so that in the event thebulb ispunctured the natural resiliency of the bellows willcause it tolexpandldue to the admission of air pressure and'the'expanding bellowsywill cutotftheheater. f. 1 ,w `m- Y The mode of securing the controlbulb to the leg3113 is shown in Fig. 8. A pair of two-part clamps 150are employed and the clamping :members are heat insulated from the leg113 and the bulb 113a `by a -layer vof heat insulation such as abersheet. f f1 Clamping members 151, 152 have partially cylindricalformations at each end of the' proper size'to engage the leg 113 and thebulb 113a.- l, Y

Screw bolt 153 passes through the clampingmernber 151 and is threadedinto a tubularformationin clamp 152, but is kept out of 'contact withthe heater. The heat insulation provides a suitable time lag betweenvtheheating of leg' 113 and the heating of bulb `11311. v

The electric heater 130e is preferably of the type having an electricheating element which is insulated by a heat resistive powder from anouter tubularVcasing-which may be made of copper or aluminum. v u Y Theclamp 130 is bent tightly about such a metal clad electric heater formaximum heatrconduction of heat ,to the enlargement 117 andtheliquidrefrigerant,contained therein. Y Y. Q l

Theinlet to the evaporator from .the compressor, condenser and capillarytube is indicated Vby the capillary end 131 of the inlet tube 132,extending'horizontally on the side23, Fig. 2. Y Y

This inlet extends behind theevaporatorwhere it is curved laterally andupwardly at 133, having aportion 134 extending upward to the` shelflevel, whereitis curved forwardly toward the shelf at 135, Fig.r2. n

The inlet tube extends through the back wall at 136, Fig. 3, andforwardly to theV curve 13 7," whichturns `'the tube toward theeasy.bend,104, V 'y ,y

A short portion 138 extends totlrefeasybendJ104, where the tube 138 maybe tapered at 139;.t0'a capillary ,end which communicates at 140 withthe tube 104 at the U-shaped bend. Thus the refrigerant is introducedinto the tubing of the shelf adjacent .the rear wall, and it travels intwo parallel paths as follows:

d From the inlet 140 the refrigerant travels forwardly across the bottomof the shelf, as indicated by the arrows, through the tubing portions103, 102, 101, 100, 99, 98, 97, 96, 95, 92, 91 and 90.

Thereafter the refrigerant in this path passes down the sinuous coils73, Fig. 4, as follows:

90, 89, 88, 87, 86, 85, 84, 83, to the bottom coils 72 of theevaporator, beginning at 82. From the point 82 the refrigerant passessinuously back and forth from side to side across the bottom of theevaporator in the coils 72, ending at 81, Fig. 4, Fig. 2.

From 81 the refrigerant passes upward through coils 80, 79, 78, 77, 76,75, entering the receiver 46 at 74.

The other parallel path of the refrigerant from the inlet point 140extends across a rear pass 105, below the shelf, emerging at 106 andextending downward at 107 to the bottom 26, inward across the bottom at109 to the point 110, backward at 111, downward at 112, downward in leg113, turning upward lagain at 114, 115, through enlargement 117, upwardat tube 120, bending laterally at 110, across the bottom to the side 23at 121, upward at 123, upward at 124, 125, 127, and into the receiver 56at 128.

, The brackets 32, 33 for the top of the evaporator have their upperanges provided with rearwardly open slots 141, Vso that depending headedfasteners carried by the liner may be received in the slots 141 as thevevaporator is pushed backwardly into the liner.

The rear wall 142 of the liner is preferably formed with a pressedgroove 143 of suicient size to receive the legs 113, 117, and the heaterand these are covered in the groove 143 by means of a cover plate 144.

The groove 143 in the liner is provided with a plurality of bowedmetalstraps 154, secured tothe liner inthe groove at each end rivets, forengaging the U-shaped legs 113, 117 and spacing them from the liner inthe groove to minimize the transmission of heat to the liner duringdefrost.

The cover plate 144- may consist of an elongated substantiallyrectangular molded plastic member formed on its back side with alongitudinally extending groove `156, and providedat its top with anopen top funnel 157. The cabinet may be provided with a suitable driptray, larger in area than the bottom of the evaporator for receiving'dr'i'ppage from the evaporator and discharging the water from a rearspout.

The funnel 157 is adapted to receive condensate which comes from thedischarge spout and runs down the groove v143 to the bottom of theliner. The water runs out of a drain in the bottom of the liner into asuitable evaporation pan (not shown) below the cabinet, where it isevaporated into the surrounding air.

The front of the evaporator is preferably closed by means of an innerevaporator door 158. The evaporator door 1'58 may consist of asubstantially rectangular molded plastic member provided with aninwardly extending border flange 159, all about its edge and with aseparate handle 160 projecting downward on the front 0f the door andsecured to the door by an `angular attaching flange 161 and screws 162.

The inside of the door 158 may be closed by means of a back panel,having inwardly extending border anges A164, the two border anges beingsecured together by a plurality of screws 165, thus providing a head airspace inside the doorf158.

The` back panel 163 may have a pair of circular holes 166 for receivingcircular rubber bumpers 167, the head 16S of which lies on the inside ofthe door in position to engage the front side edgesof the evaporator.

TheV rubber bumper167 has a reduced shank fitting` in the hole 166, anda smaller pointed head 169 which may be forced through the hole 166until the back panel is located between the two heads 168 and 169 tosecure the bumpers in place.

The door is provided on each side adjacent the lower edge with a stopbracket 170, secured to the door edge by a plurality of screw bolts 171,and having an outwardly turned flange 172 to act as a stop by engaging ahinge bracket 173 when the door is open at substantially horizontalposition.

Stop bracket 170 also serves as a hinge arm and has an apertureregistering with an aperture in the border flanges 159 and 164 forreceiving the trunnions 174. Trunnions 174 are carried by the hingebrackets 173 by having a reduced end riveted over at 175, outside thehinge bracket.

The hinge brackets 173 have a body 176 for supporting the trunnions, anoffset at 177 and an attaching ange 17S, which is secured to the linerwall. Thus the door 158 is pivoted on the liner wall and is preferablyof sufricient width to cover not only the evaporator but the spacebetween the evaporator and the liner, substantially closing the upperfront of the liner at the evaporator.

The door trunnions 174 are preferably provided with axially extendingdiametric slots 179 and a torsion spring wire 180 extends from end toend of the bottom of the door, and has a V-shaped portion 181 at eachend anchored against rotation in the slots 179.

The extreme end 182 of the wire extends into a bore in the trunnion 174.The torsion wire 180 is bent upward to the point 183, where it is bentdownward and provided with an open U-forrnation 184, which is anchoredxedly to the door by means of a bracket 185 and a screw bolt 186.

The U-shaped formation 184 turns with the door while the V-shapedformations 181 are held fixed by the trunnion slots. Spring 180 is underinitial torsion, tending to hold the door closed when it is closed andits tension is increased when the door is opened through 9() degrees,but is not suiiicient to close the door from the fully open position.

The details of the door are not of my invention and any suitable type ofevaporator door may be used.

The refrigerating system of the present refrigerator is shown in Fig. 9.It includes a motor compressor 187, having an upper motor housing 188,joined to a lower oil sump 189, surrounding a motor compressor 190,directly driven by the motor shaft. Y

The outlet 191 of the compressor is connected by conduit 192 to thecoils 193 0f a separate precooling condenser section having heatdissipating tins or wires 194.

The precooler coils 193 are connected by conduit 19S to the top of themotor housing to carry back the partially cooled and condensedrefrigerant and oil to the top of the motor housing, where it drainsdown through the motor parts, the oil settling in the oil sump 189.

There is some revaporization of refrigerant in the motor housing incooling the motor parts 196. The refrigerant passes from the top of themotor housing 188 by conduit 197 which leads to the main condenser coils198, which may be provided with heat dissipating fins 199 or wires ormay be any other suitable form of condenser.

From the main condenser coils 193, the now liquid refrigerant may passthrough a drier 200 and through a capillary tube 131 to the inlet of theevaporator, indicated at 140.

The course of the refrigerant through the evaporator has already beendescribed in two parallel paths which lead to the receiver 55.

The suction tube 66 extends from the receiver 56 to the inlet 201 of themotor compressor.

Referring to Fig. lO, this is a wiring diagram of one form of manualcontrol for the refrigeration system. In this diagram 187 indicates themotor compressor, which is usually of the induction type having threeconductors 202 CFI ' 8 leading to a starter switch 203 for controllingstarting windings and running windings.

One conductor 204 leading from the starter switch passes through theusual thermostatic controlling switch 205, 206, having a bulb mounted onthe evaporator shelf and adapted to start the motor compressor wheneverthe shelf rises above a predetermined temperature, which is always belowfreezing.

The thermostat, usually called the cold control, is connected byconductor `207 with the refrigeration contact 210 of a defrost controlswitch. The defrost control switch has a movable cotnact arm 209, whichis shown in the heater position engaging heater contact 20S. Y

Contact arm 209 is connected by a conductor 211 to the usual llO voltlighting circuit. The heater contact 208 is connected by conductor 2,12to the heater coil a, the other end of which is connected to the otherline conductor 213.

The line conductor 213 also extends to the starter switch 203.Themovable contact arm 209 may be moved by a plunger 214 against spring215 to the heater position as shown, where it-may be latched by alatching lever 216 pivoted at 217, and urged into latching position byspring 218. Y

A ther-mostatic bellows 219 isl connected by a capillary tube 220 to thebulb 11341,v which is fastened to the leg 113 of the evaporator. Thusthe defrost may be initiated by pressing on the plunger 214 manuallycompressing the spring 215, and latching the plunger in the heaterposition.v

When the bulb113a is heated sufficiently the thermostat 219 will unlatchthe plunger 214 and cause it to move back into engagement with therefrigerator contact 208, cutting out the heater 130e: and restoring thesystem to controlI of the usual cold control thermostat 205, 206;,

The operation of the system is as follows: When the cold controlthermostat 205, 205 has its bulb elevated at temperature toapredetermined point, which is still below freezing, the motor compressoris started and it compresses refrigerant which is carried away from themotor compressor 187 to a condenser precooling coil 193, where it ispartially condensed and returned to the top of the motor housing.

The refrigerant then passes from the top of the motor housing to themain condenser 198 where it is condensed and passed through the drier200 and through the capillary tube to the evaporator inlet at the rearof the evaporator shelf.

The refrigerant passes in two parallel paths through the evaporator, therst path being forwardly through the sinuous coils of the shelf whichare cooled to an ultra below-freezing temperature capable of maintainingfrozen food in a frozen condition at all times.

From the shelf front end the refrigerant passes outwardly to the leftside of the evaporator and down the sinuous coils to the bottom. It thenpasses through the sinuous coils on the bottom of the evaporator andupward through sinuous coils on the right side of the evaporator to thereceiver 56.

The other parallel path from the evaporator inlet 140 is across theevaporator shelf through a straight pass 109 downwardly through tubing107, on the left side of the evaporator, to the depending evaporator leg113, upwardly in the leg 117 and across the bottom of the evaporator at121, and upwardly through conduit 125 to the receiver 56.

The refrigerant vapor is pumped off the top of the receiver 56 throughsuction tube 66, which leads back to the inlet of the motor compressor187.

When itis desired to defrost the evaporator, all parts of which arepreferably maintainedy at a below-freezing temperature,'the user maypush the plunger 214, moving the defrost switch arm 209' to break thecontact 210 and engage the contact 208, which closes the circuit throughthe heater 13011. This stops the motor compressor during defrosting bybreaking the motor compressor circuit, and the defroster contact arm 209is latched in the heater closed position.

The heater 130a by heat conduction heats the refrigerant in the enlargedtube 117, causing it to boil upward and to circulate up the tube 121,124, 126 to the receiver 56. Hot refrigerant may run down from receiver56 through the sinuous tubing on the right side of the evaporator, shownin Fig. 2, through the sinuous tubing 72, on the bottom of theevaporator, and up the sinuous tubing 73 on the left side of theevaporator.

From thence the hot refrigerant passes into the tubing on the evaporatorshelf which communicates with the downwardly extending leg 113, leadingthe hot refrigerant back to the heated leg 117.

As the hot refrigerant circulates it heats the evaporator coils andadjacent evaporator casing, which are progressively heated until theymelt all the frost from the evaporator. When the refrigerant is stillhot at the time it arrives at the upper part of the tube 113, it heatsthe bulb of the cutoff thermostat 219, which expands and unlatches thelatch 216, permitting the spring 21S to move the plunger back to therefrigeration contact and breaking the heater circuit at the heatercontact 208.

In the event of a failure of the circulation of refrigerant the bulb112m is, nevertheless, heated by radiation due to its proximity to theheater, the upper end of which is the hottest, and the heater circuit isbroken before the evaporators or other parts are so overheated that theymay become damaged.

In the event of failure of the thermostat 219 by a puncture or loss ofits volatile uid, this thermostat is preferably filled with refrigerantat subatmospheric pressure so that the air will leak in and cause it toexpand and cut off the heater in this event also.

Thus the present system is safe against damage to the evaporator byoverheating by the electric heater element. When the defrost isterminated the system is again` restored to the normal coldcontrolthermostatic switch 205, 206, and refrigeration proceeds as before.

The shelf is the last part to be heated and defrosted so that frozenfood inside the evaporator is subjected to a minimum amount of heat, andthe defrost is accomplished so quickly that the frozen food is notmelted or heated to any appreciable extent.

It will thus be observed that I have invented an improved defrostingevaporator and an improved defrosting refrigerator and refrigerationsystem, in which heat is applied to depending tubing connected with thetubing of the evaporator in such manner as to cause the circulation ofhot refrigerant throughout the evaporator until all the frost is meltedfrom the evaporator and the freezing shelf is last to be defrosted sothat the adjacent contents are subjected to a minimum amount of heat.

While I have illustrated a preferred embodiment of my invention, manymodifications may be made without departing from the spirit of theinvention, and I do not wish to be limited to the precise details ofconstruction set forth, but desire to avail myself of all changes withinthe scope of the appended claims.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent of the United States, is:

1. In a defrosting system for a household refrigerator, the combinationof an insulated cabinet, comprising an outer metal shell, an innerliner, and insulation between them, said cabinet having a door opening,and an insulated door, an evaporator comprising a substantially U-shapedmetal casing provided with a transverse freezing shelf, said evaporatorbeing supported from the top of the liner, below freezing coils on thebottom of the shelf for producing an ultra-below freezing zone above thewasn shelf, below freezingcoils'on the sides and bottom of said casingfor cooling the space outside said evaporator to an above-freezingtemperature, and the space inside the evaporator, below the shelf, to abelow-freezing temperature, and a depending U-shaped leg of tubingconnected to said coils, and having an electric heater applied to one ofthe branches of said U-shaped leg, for heating the refrigerant andcausing it to circulate upward in the heated branch and downward in theother branch, the hot refrigerant heating all the evaporator coils andcasing and melting the frost on them, and a cut-off thermostatic switchin circuit with said electric heater, and having a bulb connected to theunheated branch adjacent said heater, to be heated by conduction andradiation in the event of a failure by circulation of the refrigerant,said bulb being secured to said unheated branch by opposed clampingmembers, and a layer of insulation interposed between the said clampingmembers and said bulb and branch to produce a time lag in the heating ofsaid bulb by radiation and conduction from said heater.

2. In a defrosting system for a household refrigerator, the combinationof an insulated cabinet, comprising an outer metal shell, an innerliner, and insulation between them, said cabinet having a door opening,and an insulated door, an evaporator comprising a substantially U-shapedmetal casing provided with a transverse freezing shelf, said evaporatorbeing supported from the top of the liner, below freezing coils on thebottom of the shelf for producing an ultra-below freezing zone above theshelf, below freezing coils on the sides and bottom of said casing forcooling the space outside said evaporator to an above-freezingtemperature, and the space inside the evaporator, below the shelf, to abelow-freezing ternperature, and a depending U-shaped leg of tubingconnected to said coils, and having an electric heater applied tov oneof the branches of said U-shaped leg, for heating the refrigerant andcausing it to circulate upward in the heated branch and downward in theother branch, the hot refrigerant'heating all the evaporator coils andcasing and melting the frost on them,said casing having a rear wallclosing the rear of the evaporator, said rear wall having drainageapertures at the shelf level and the bottom level of said evaporator,for draining condensate.

3. In a defrosting system for a household refrigerator, the combinationof an insulated cabinet, comprising an outer metal shell, an innerliner, and insulation between them, said cabinet having a door opening,and an insulated door, an evaporator comprising a substantially U-shapedmetal casing provided with a transverse freezing shelf, said evaporatorbeing supported from the top of the liner, below freezing coils on thebottom of the shelf for producing an ultra-below freezing zone above theshelf, below freezing coils on the sides and bottom of said casing forcooling the space outside said evaporator to an above-freezingtemperature, and the space inside the evaporator, below the shelf, to abelow-freezing temperature, and a depending U-shaped leg of tubingconnected to said coils, and having an electric heater applied to one ofthe branches of said U-shaped leg, for heating the refrigerant andcausing it to circulate upward in the heated branch and downward in theother branch, the hot refrigerant heating all the evaporator coils andcasing and melting the frost on them, said casing having a rear wallclosing the rear of the evaporator, said rear wall having drainageapertures at the shelf level and the bottom level of said evaporator,for draining condensate, said casing having its side walls slightlylonger in a vertical direction at the rear of the evaporator, causing adownward tilt of the shelf and the bottom toward the rear drainageopenings.

4. In a defrosting system for a household refrigerator, the combinationof an insulated cabinet, comprising an outer metal shell, an innerliner, and insulation between them, said cabinet having a door opening,and an insulated door, an evaporator comprising a substantially U-shapedmetal casing provided with a transverse freezing shelf, said evaporatorbeing supported from the top of the liner, below freezing coils on thebottom of the shelf for producing an ultra-below freezing zone above thesi ei, below freezing coils on the sides and bottom of said casing forcooling the space outside said evaporator to an above-freezingtemperature, and the space inside the evaporator, below the shelf, to abelow-freezing temperature, and a depending U-shaped leg of tubingconnected to said coils, and having an electric heater applied to one ofthe branches of said U-shaped leg, for heating the refrigerant andcausing it to circulate upward in the heated branch and downward in theother branch, the hot refrigerant heating all the evaporator coils andcasing and melting the frost on them, a drip pan carried by the linerWalls under said evaporator for receiving con- .,sate from theevaporator, said pan discharging into a funnel carried by the rear wallof the liner, said rear w 'i having a pressed groove for receiving saidleg and Mtl tonnel discharging into said groove.

5. In a defrosting system 4for a household refrigerator, the combinationof an insulated cabinet, comprising an outer metal shell, -an innerliner, and insulation between them, said cabinet having a door opening,and an insulated door, an evaporator comprising a substantially U-shaped metal casing provided with a transverse freezing shelf, saidevaporator being supported from the top of the liner, below freezingcoils on the bottom of the shelf for producing an ultra-below freezingzone above the shelf, below yfreezing coils on the sides and bottom ofsaid casing for 4cooling the space outside said evaporator to anabove-freezing temperature, and the space i11- side the evaporator,below the shelf, to a below-freezing temperature, and a dependingU-shaped leg of tubing connected to said coils, and having an electricheater applied to one of the branches of `said U-shaped leg, for heatingthe `refrigerant and causing it to circulate upward in the heated`branch and downward in the other rbranch, the hot refrigerant heatingall the evaporator coils and casing and melting the frost on them, adrip pan carried by the liner Walls under said evaporator for receivingcondensate from the evaporator, said pan dischargingpinto a funnelcarried by the rear wall of the liner, said rear wall lhaving a pressedgroove for receiving said leg Iand said tunnel discharging into saidgroove, and a cover for closing the front of said groove and coveringsaid leg.

6. In a defrosting system for a household refrigerator, the combinationof an insulated cabinet, comprising an outer metal shell, `an innerliner, and insulation between them, said cabinet having a door opening,and an insulated door, an evaporator comprising a substantially U-shaped metal casing provided vvith a transverse freezing shelf, saidevaporator being supported from the top of the liner, 'below freezingcoils on the bottom of the shelf for producing an ultra-below Ifreezingzone above the shelf, below freezing coils on the sides and bottom ofsaid casing for cooling the space outside said evaporator to anabove-freezing temperature, and the space inside the evaporator, belowthe shelf, to a below-freezing temperature, and a depending U-shaped legof tubing connected to said coils, and having an electric heater appliedto one of t-he branches of said U-shaped leg, for heating `therefrigerant and causing it to circulate up-ward in the heated branch anddownward in `the other branch, the hot refrigerant heating all theevaporator coils and casing and melting the frost on them, said linerhaving a vertically extending pressed groove in its rear wall, and saidU-shaped leg extending rearwardly to said groove and vertically in saidlgroove of said liner and conveying condensate along lthe tubes down saidgroove, and a cover member `for said groove, said cover including anupper funnel formation, and Iforming a conduit for condensate in saidgroove.

Atchison Aug. 4, 1942 Duncan et al. Oct. 6, 1953

